Electronic card assemblies are tested prior to shipment with a vacuum test fixture. The cards are tested by inserting a probe into the card edge connector by means of a pneumatic actuated Side Access Unit (SAU). The force created by the SAU displaces the card in the same direction of the force being applied. This movement can cause the test probes in the test fixture to become perturbed or misaligned with the test pad of the card being tested, preventing adequate probe contact with the test pad.
Test pads on the electronic card require precise alignment, and are located on 25 mil and 50 mil centers. The test pad diameters are small, as little as 20 mils in diameter. Therefore, the test probe of the SAU, when misaligned by as little as 0.003" to 0.005" due to test pad movement, can result in testing inaccuracies.
It has been suggested that stationary, or permanently located mechanical stops could be used to oppose the SAU-generated displacement. However, the dimensional tolerances of the finished edge of the electronic card are too great for this scheme to work.
The present invention reflects the discovery that a card edge opposer cam assembly can provide a mechanical stop having a zero tolerance. The opposer cam of the assembly is pneumatically actuated from a common pneumatic system that serves the SAU. The opposer cam is placed against the edge of the electronic card opposite the edge associated with the SAU. This occurs before the SAU is pneumatically engaged. In this manner, the force generated by the SAU is prevented from moving the card test pads out of alignment with the probes.